1. Field of the Invention
The present invention relates to a signal receiver of the Global Positioning System (GPS) and a demodulation processing control method, and more particularly, is suitably applied to such as a signal receiver of GPS for measuring the positioning of mobile units.
2. Description of the Related Art
Heretofore, in the GPS satellite signals to be transmitted respectively from the plural number of GPS satellites revolving about over the earth are received by the GPS signal receiver, and by analyzing said satellite signals received, the distance between said GPS signal receiver and each GPS satellite is obtained and based on this, the present position of the mobile unit is calculated.
The satellite signals to be transmitted from these GPS satellites are the signal spectrum diffused by the pseudo noise (PN) code formed of a series of codes of different types in each GPS satellite.
Accordingly, the GPS signal receiver can generate local PN codes corresponding respectively to multiple kinds of GPS satellites, and secures synchronism by matching the phases of the local PN codes generated with the phase of the PN code of the satellite signal. And after adding synchronism by tracking the satellite signal by applying an inverse spread spectrum processing, the GPS signal receiver demodulates the navigation message (such as orbit information for positioning measurement) from the GPS satellite.
For example, as shown in FIG. 1, the GPS signal receiver 1 receives satellite signals S1 to S4 to be transmitted from the plural number of the first GPS satellite 2 to the fourth GPS satellite 5 via a GPS antenna 6 and a signal receiver circuit 7, and supplies the satellite signal S1 to the first demodulator 8, the satellite signal S2 to the second demodulator 9, the satellite signal S3 to the third demodulator 10, and the satellite signal S4 to the fourth demodulator 11.
The first demodulator 8 to the fourth demodulator 11, after acquiring synchronism and adding synchronism to the satellite signals S1 to S4, applies the inverse spread spectrum processing, and demodulates the satellite signals S1 to S4. And as well as transmitting the demodulation result data S5 to S8 to the circuit of the latter stage (not shown in Fig.), the first demodulator 8 to the fourth demodulator 11 transmit these to the control circuit 12.
The control circuit 12 assumes the demodulation condition of the first demodulator 8 to the fourth demodulator 11 based on the demodulation result data S5 to S8 to be supplied from the first demodulator 8 to the fourth demodulator 11, and by supplying the demodulation control signals S11 to S14 according to said demodulation condition to the first demodulator 8 to the fourth demodulator 11, it controls the demodulation condition in the first demodulator 8 to the fourth demodulator 11.
With this arrangement, the GPS signal receiver 1 calculates the distance between multiple GPS satellites by demodulating satellite signals S1 to S4 from the first GPS satellite 2 to the fourth GPS satellite 5 at the first demodulator 8 to the fourth demodulator 11 in parallel respectively. And based on the distance relation between these, the current position will be measured.
In the GPS signal receiver 1 thus constructed, since synchronism acquisitions are conducted to satellite signals S1 to S4 from the first GPS satellite 2 to the fourth GPS satellite 5 respectively, it is required to have the same number of demodulators as the number of GPS satellites existing in the signal receivable range (the first demodulator 8 to the fourth demodulator 11) or more than that number of demodulators. And this has created a problem that the circuit construction has become large-sized.
Moreover, since the GPS signal receiver 1 operates the first demodulator 8 to the fourth demodulator 11 simultaneously in parallel as shown in FIG. 3B, it has created a problem that the consumption of electric power has increased.
In view of the foregoing, an object of the invention is to provide a signal receiver of GPS with small sized and consuming few electric power and demodulation processing control method.
The foregoing object and other objects of the invention have been achieved by the provision of a signal receiver of GPS. Satellite signals to be transmitted are received from multiple satellites respectively in the GPS and the demodulation processing of the satellite signals by means of demodulation means is time division controlled based on the demodulation timing to each of said satellite signals received. In this way, the demodulation processing can be executed without providing the demodulator corresponding to each of satellites.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.